1. Field of the Invention
The present invention is generally related to switches which are activated and deactivated in response to changes in the inclination of the switch and, more particularly, to a tilt switch that incorporates a fulcrum and lever system with a movable weight disposed on the lever.
2. Description of the Prior Art
Many different types of tilt switches are known to those skilled in the art. Perhaps the most well known is the mercury tilt switch which utilizes a globule of mercury in a sealed vial which, when tilted, causes the mercury to move from one end of the vial to the other and to conductively bridge two conductors which are disposed within the vial.
Bitko U.S. Pat. No. 4,135,067, issued on Jan. 16, 1979, discloses a tilt switch which is omnidirectional and which includes an enclosure for a gravity response conductive ball. It provides an annular shelf that surrounds a central depression where at least one switch contact passes into the housing and is exposed. In response to the tilting of this switch, a ball is moveable away from a cup shaped housing to the depression where it engages the contact and closes a circuit between that contact and another contact. This particular device incorporates a globule of a conductive liquid, such as mercury, within its housing for the purpose of conductively bridging the two contacts.
Roberts U.S. Pat. No. 4,297,683, which issued on Oct. 27, 1981, describes an alarm system for parking meters. The unauthorized entry into a portion of the device, such as the parking meter, utilizes a radio transmitter which is adapted to send two signals simultaneously to a receiver that is constantly energized. A switch is actuated when the supporting post of the parking meter is bent and a timer is placed in the circuit so that only after a determined interval of time a signal is sent which indicates the bent post. This device utilizes a rolling member, such as a sphere, inclosed in a housing.
Maples U.S. Pat. No. 4,833,281, which issued on May 23, 1989, discloses a motion detector that is particularly applicable for use with a transmitter in motor vehicle keyless entry system. The motion detector includes a spool surrounded by and electrically insulated from a shell. A sphere is positioned in the annular cavity around the spool. Changes of state of the motion detector occur when the ball moves into and out of direct contact with the spool or shell and further as the ball rolls around the annular cavity while being supported by both the spool and shell caused by surface roughness of the interface surfaces.
Cheshire U.S. Pat. No. 4,789,922, which issued on Dec. 6, 1988, describes an earthquake safety light which utilizes a weighted object which is displace on the occurrence of an earthquake of a given preset magnitude and, when it is displaced, it closes a circuit which activates an emergency light so that occupants in the surrounding area may see the light and be guided by it.
Viator U.S. Pat. No. 4,697,174, which issued on Sep. 29, 1987, discloses a ball actuated alarm device that provides a warning at the initiation of catastrophic tilting of a device such as an offshore platform. The alarm device utilizes a free rolling ball member on a normally horizontal planar surface. The surface is divided into regions by elongated protuberances which separate the ball from a switch that is capable of being closed by contact with the ball.
Canevari U.S. Pat. No. 4,628,160, which issued on Dec. 9, 1986, describes an electrical tilt switch that comprises a cylindrical cap member with a hollow interior and an internally extending ridge positioned a significant distance above its lower edge. It also comprises a spherical contact member that is carried on a dished surface and movable against the ridge when the switch is tilted to a specified angle. For severe environmental conditions, the preferred material for the cap, the base and the spherical contact member is a Monel alloy.
Several problems exist with regard to tilt switches known to those skilled in the art. First, the switches which utilize a conductive globule of liquid sometimes require particular care in their use. Furthermore, switches which incorporate a conductive rolling sphere which makes electrical contact with two conductors and provides an electrical bridge between those conductors are sometimes limited in application to currents below a certain magnitude. If the switch is required to be responsive to very small degrees of inclination, pitting of the sphere's surface inhibit the sphere from rolling at extremely low angles of inclination. The pitting forms numerous marks on the sphere's surface as a result of electrical arcing when contact is being made or broken between the electrical conductors and the sphere These small defects to the smoothness of the sphere surface can inhibit the smooth rolling of the sphere and, under some conditions, prevent the sphere from initiating its rolling movement on a track when the required angle of inclination exits.
Another severe problem which exists in most tilt switches that incorporate a rolling member is that the force that is available to make and break an electrical contact is generally only a small fraction of the weight of the sphere. In some applications, it is desirable to close electrical contacts and hold them together with a force that is equal to o greater than the weight of the sphere. Conversely, it is also desirable to have a force available to break the contacts (in case of welding or sticking) that is equal to or greater than the weight of the sphere. It is also desirable to provide an inclination sensitive switch which does not use the surface of the sphere as an electrical contact and, therefore, eliminates the possibility of pitting and failure of the switch due to the defects in the spherical surface caused by that pitting.